Does anyone know why or how upcoming anniversary or years of service would be sent to employees emails and not the one on file?

You can manually email your employees outside of QuickBooks Online, Amy.

Although it's great to have options for automating emails to acknowledge employees' years of service or upcoming anniversaries, this feature is currently unavailable in the program. These details weren't sent out directly from QuickBooks.

For now, you can utilize your external emails to send these acknowledgments to your employees as a workaround. This way, they can still receive important communications through their personal addresses.

Additionally,  I'm including this guide in case you want to track your overall business finances: Run a report.

Please let us know below for any additional queries.

@FateCandylaneT  RE: You can manually email your employees outside of QuickBooks Online, Amy.

That's not an answer to the OP's question. Not even close. It seems you didn't read and/or don't understand the question.