Reconcilling broken

[Wes Gray]

I've previously had no trouble reconcilling my bank statement, then
last time I went to do it the beginning balance gnucash gave me was
way low.  I can't tell why.  The only thing I can think of is that
I have replaced some previously reconcilled entries with
non-reconcilled ones.  Looking at the entries up til the last
reconciliation shows them all reconcilled except a few.  Is there
a way to manually set them?  Is there any other way to "go back"
to a previous statement and start reconcilling over again?