Although i'm not personally familiar with the "standard series seed" documents, I would think this problem could be easily avoided through appropriate application of copyright to the original documents.

Something to the effect that the document may only be amended in certain ways which would be apparent on reading the amended document (ie. all amendments must be made by way of special condition).

Allowing investors to make changes to "standard" draft documents which will only be picked up by experienced startup lawyers defeats the purpose of having those standard form documents.

EDIT: fixed grammatical error.