The present plan for difference imaging is to use roughly annual templates. With the plan for re-computing difference-imaging data products in Data Releases, we should understand how we will support users who wish to stitch together a full multi-year relative-photometry light curve from the results.
There are a range of possibilities of levels of hand-holding that we might provide. The answer affects whether properly "stitched" light curves would be available, e.g., through a TAP service and/or the Portal, or only as a user-derived data product in the Notebook Aspect requiring the user to perform the cross-normalization themselves based on some auxiliary zero-point information provided.
A closely related issue applies, perhaps with modest additional complications, for joining Data Release difference imaging photometry to the "live" Prompt DIASource records.