It's very doable to add without it and my experience is I've often worked with models trained online where the data has a retention of a few months so any old e

It's very doable to add without it and my experience is I've often worked with models trained online where the data has a retention of a few months so any old enough model will have been trained on data points that don't exist anymore. Large tech companies tend to not keep all data for a mix of storage cost, lower value for some domains (for recommendations freshness is quite useful), and various privacy concerns. Privacy alone means you should have ways to delete data entirely for many problems. If you train with user data and the user requests to delete all info on them through gdpr that includes your training data. I can't remember the amount of time gdpr allows for deletion (I think 30 days or maybe 60), but if you keep a lot of your data with a lower retention than that by default that makes deletion a lot easier. There is other data that has naturally very long retentions (sales orders) where even with deletion requests some aspects should be kept just for financial compliance.