I'm sorry you found out the hard way.  If you were using Paperless Office, you can have that paperwork saved when it's printed.  If your reseller cannot give you training on your new system, you can check out SageU.com - they have training on pretty much every aspect of Sage 100 (I see a Bank Rec course if $59, currently).

I would recommend you setup all journals and registers to go to paperless office to help prevent this issue in the future and make sure you do NOT allow updating journals from preview.

We have all our registers use Paperless office so they are saved as PDFs. Even the bank reconciliation, which we attach to the GL account as a memo each month, so it's easy to find. (We do the same with the A/R and A/P reconciliations.)

So if you can not go back and print old bank reconciliations (or how do you know if 'Paperless Office' was/is turned on?) - how do you know the last time one was completed? Sorry, brand new to Sage for a company very behind on their books. When you open the 'Reconcile Bank' module and select the account you want to reconcile, it comes up with a number in the ending statement balance box, which can be changed, is the number defaulted/shown, is that the ending statement balance from the last time the account was reconciled. Any guidance/help is much appreciated, this system doesn't seem to be real intuitive/user friendly but hopefully it get's better. Any beginner pointers/courses suggested to get up to speed would also be appreciated. Thanks!

Once the bank rec is completed, if you purged cleared transactions and did not save that report, then it is gone forever.

Write a Crystal report based on the AP_CheckHistoryHeader and include the ClearBank and ClearedDate fields to find out which checks were cleared on what date.  You can also edit the AP Check History Work table to add these fields to the works table and then add the fields to the report.