I can't respond for all vendors, nor for the store proper, Pinotage, but I will provide you with our own response to the question:
If E.N. Publishing ever re-releases product in P&M format, we'll be sure to say so on the P&M product in question that it is material from product X. For example, in "Instant Bawdy-Houses" Pick and Mix product, we state clearly in the extended description that the example stats for courtesans and madams are excerpts from Everyone Else. However, we have no intention at this time of taking material from our full-length releases and re-issuing them in P&M format - only of using some such material as supplemental material for our P&M releases (like the above example).
On the other hand, in time we are likely to take some material from P&M and reissue them in full length releases. In those cases, we will definitely update the description of the P&M to say it is also included in product X, as well as indicating in product X that it contains the contents of P&M products Y and Z.