Uncleared / reconcile relationship

So I've been using YNAB for a couple months and generally I've been reconciling at least weekly.

Everything was lining up great until just recently when one of my accounts seemed to be out of sync, and I'm not sure why.

So today I tried again and noticed that all my bank transactions were cleared at the bank, so would have thought this would settle any discrepancies (my last successful reconcile was prob a week or so ago, before it seemed to get out of sync)

I read the reconcile document that was recommended inside YNAB and got a better understanding of the grey vs. green cleared icon.

It said for any really old transactions still with the grey icon - that I could manually clear them and do the adjustment, so this is what I did.

Now everything is back in sync and it did a balance adjustment and gave me like $200 back to ReadyToAssign.

Some of the manually cleared transactions went all the way back to November. So I think those could possibly be cases where I pre-entered the transaction but it didn't match the actual charge (Walmart is notorious for this) - so that all makes sense. It could mean I pre-entered a $45 Walmart order, but then only got charged $36 because something was out of stock. That would then cause that $45 entry to hang out in YNAB and never clear.

So my biggest question is -- how were these transactions sitting there this long ïn the uncleared grey state - yet I was able to successfully reconcile this account every week until just recently?

Moving forward I'm gonna keep a closer eye on these grey icons - tecnically they should all clear within a few days or else something might be wrong (amount changed, etc)