RecordID should not be used as a primary key.
RecordID is a serial number starting with one that is generated when the record is created. Thus records created in a different table may very likely have a record ID that matches records in the first table.
Furthermore, if you import the records, say from a backup into a clone, the imported records all get new record ID's which may be different from their original values.
I recommend auto-entered serial numbers for this. If you need it to be unique from records created in a different table, specify a different prefix or suffix to records created in each table.
You could set the next serial value to 1A, on one table and 1B in the other for example.