Nominal vs. effective sampling rate

[cbrnr]

I recently worked with an XDF file containing two streams, an EEG stream and a marker stream. I noticed that when using the nominal sampling rate (e.g. 1000 Hz), the two streams drift over time when the effective sampling rate differs (even slightly). In my data, the effective sampling rate was 1000.01218...Hz. At the end of the recording, this differences adds up to several milliseconds.

This difference can be problematic if I want to match marker stream events to events (e.g. spikes) in a channel in the EEG stream, because their difference will increase with time. Therefore, I was wondering if I should just use the effective sampling rate for the EEG stream. Is this a good idea? What is more precise, the nominal sampling rate claimed by the amp or LSL time stamps (which in most cases will use standard computer clocks)?