## Issue Addressed
#4331
## Proposed Changes
- Use comparison rather than strict equality between the earliest epoch we know about and the backfill target (which will be the most recent WSP by default or genesis)
- Add helper function `BackFillSync<T>::would_complete` to achieve this in one location
## Additional Info
- There's an ad hoc test for this in #4461
Co-authored-by: Age Manning <Age@AgeManning.com>