Completed Days and Google Fit/Device Syncing?

Hi, I have noticed that if I do not manually go into Google Fit on my phone, it will occasionally fail to sync my activities and measurements/metrics with Cronometer on its own.

My question is, does marking a day "completed" still allow Google Fit (or other devices) to update a past day? Or does marking it complete prevent even Google Fit or my devices from updating with data once it finally gets around to syncing?

Thanks!