Constitution and Strong Coincidence

I was rereading Ryan Wasserman's 'The Standard Objection to the Standard Account' for a seminar on material constitution that I'm teaching this term. In it, Wasserman considers a number of "mereological" solutions to the "standard objection" (i.e. since Lump and David share all of their microphysical parts, there is nothing to explain their difference in kind and de re modal and temporal properties). Wasserman considers three responses to that objection: the no coincidence response (Lump and David share no parts), the weak coincidence response (Lump and David weakly coincide, which essentially boils down to the fact that all parts of Lump are parts of David but some parts of David (e.g. its arm) are not part of Lump), and the strong coincidence response (Lump and David strongly coincide share all their (material) parts at every time they both exist). While I think Wasserman's case against the first two views is strong, I'm not persuaded by his case for the third view. (In fact, I'm not even sure I understand what his proposal exactly is.)

The strong coincidence response (SCR) seems to be committed to the following claims:

1. For any time t, if Lump and David exist at t, they wholly exist at t.
2. For any time t, if Lump and David exist at t, they strongly materially coincide at t (i.e. every (material?) part of Lump at t is a part of David at t and every part of David at t is a (material?) part of Lump at t.)
3. For any time t, if Lump and David exist at t, they spatially coincide at t (i.e. every spatial part of Lump at t is a part of David at t and every spatial part of David at t is a part of Lump at t.)

So, one could wonder (at least I do) how can David and Lump differ in their parts given (1)-(3)? Since I'm not quite sure I understand Wasserman's answer, I'll let him do the talking now (I only divide the different claims and label them for the sake of the discussion):

[(a)][Both the defender of the standard account and the defender of the doctrine of temporal parts] will agree that David is a temporal part of Lump during the interval from t2 [when David came into existence] to t3 [when David and Lump ceased to exist]. For David exists only during that interval, David is a part of Lump during that interval and David overlaps during that interval everything that is a part of Lump during that interval.

[(b)] Moreover, both parties will agree that David is a proper temporal part of Lump during the interval in question since David is not identical to Lump.

[(c)]The two parties will not agree on everything, of course. Most importantly, the temporal parts theorist will assert, and the proponent of the standard account will deny, that Lump has temporal parts (during the interval from t1 [when Lump came into existence] to t2) that David lacks.

[(d)] Still, given that David is a proper temporal part of Lump, there must be some sense in which these two objects differ in parts.

[(e)] Indeed there is: Lump has spatial parts during the interval from t1 to t2 that David lacks.

I find it very hard to see how (a) and (even harder) (b) can be true. In fact, I can't see any good reason for the constitutionalist qua endurantist to hold that David is a temporal part of Lump between t2 and t3 let alone a proper temporal part of it. If one believes that Lump and David wholly exist at every time at which they exist, they would seem to have to believe that, at most, David and Lump can only have improper temporal parts at every time at which they exist (At t, if Lump exists, it is its only temporal part) but I can't see any plausible way to think that one can be a proper temporal part of the other (David can be a proper temporal part of Lump only if there are temporal parts of Lump that are not temporal parts of David, but since, given (1), it would seem that neither Lump nor David has (proper) temporal parts, I can't see how the latter can be a proper temporal part of the former).

I find it even harder to see how (b) can be true given (c). If the constitutionalist qua endurantist denies that Lump has temporal parts David lacks how can the latter be a proper temporal part of the former? According to Wasserman's (e), it would seem it can be so by virtue of Lump's having spatial parts between t1 and t2 that David does not have (after all, David doesn't exist during that period!).

Okay, so, suppose that you and Wasserman are standing in front of Lump and David and you ask 'But how can Lump and David have different kind, de re temporal and de re modal properties right now even if right now they are sharing all of their parts and their only parts are parts that exist right now?' I guess Wasserman's answer would be: 'Well, they do because they did not share all of their parts yesterday when David did not exist' But, at most this can explain why bakc then it was posssible for them to have different properties but not how it's possible now when the two share all of their parts (according to (2)).

I guess I'm missing something terribly obvious. Can anyone help me see what that something is?

(Let me mention a few other things Wasserman says that I find very puzzling:

Wasserman suggests that the standard objection applies not only to constitutionalism but also to fourdimensionalism and to the view that my hand is a spatial part of myself. But how can that be the case if the standard objection is predicated on the two objects sharing all of their parts? (of course the part of me that spatially coincides with my hand shares all of the parts with my hand (it is my hand after all!) but I don't)

And even if the standard objection applies to those views as well wouldn't that be a reason for those who hold those views to worry rather than a reason for the constitutionalist to feel relieved given that there are other views (most notably, nihilism) that are immune to that objection?

Finally, Wasserman seems to assume that a difference in temporal or spatial parts can explain a difference in kind, but I don't see any good reason to think so. There seems to be plenty of objects that differ in spatial and temporal parts without differing in kind and the reason why I am a human being and my hand is not is presumably not that I don't spatially coincide with my hands (althugh presumably it is a necessary condition for my being human).)