I’ve run into a similar problem, where the created_at date is shorter than the span provided in the tag. (Not really problem, just limitation I suppose?)
My ‘solution’ was to compare the two dates and if the difference was > 30 days, I would guesstimate the original sub date based off the ‘months’ param sent. It’s not entirely accurate as the true origial sub date can be +/- 15 days, but it’s close enough for most purposes.