Anderson window balance circa 1984

The balances for left and right have identical stamps on them.

One stamp is 11600-17. The others are E91 9#27 5-84. I'm betting 927 is the number.

I have four windows on the 2nd floor on the front of the house. Three of them need both balances replaced. Is it safe to assume that all of the balances will be the same? I really don't want to have to disassemble them all to get at the balances and then have to put it all back together again.

Thanks.