I raised concerns at the recent SAS meeting that the AAVSO's VSP (Variable Star Plotter) chart/photometry system was not able to recover old data from VSD (the comp star database), that a chartID generated a year ago, if submitted to VSP today, might get back different magnitudes for the comp stars if those stars had been updated in the interim.
This is Not true; my assertion was incorrect. And I apologize for scaring you!
If you have a chartID of the new series (ie, prefixed with and X) you can be sure that VSP will always come back with the same report, the same values. I believe this chart scheme has been in place since 2008.
My assertion was based on a cursory analysis of the database structures where I was not able to spot the relationship of timestamp-to-chartID. The code for VSP and VSD is very difficult to understand. But a simple experimental check demonstrated that old chartID's work, fetching the same values they reported when they were created.
Sorry about the alarm.
George
SGEO