Updating my resume for industry. I switched labs in grad school - what to put on my resume for this time period?
Just list it in brief. A single sentence will do it. You say 1-2 pages, so unless you’ve filled 2 pages, you should have room for one sentence (one line) to account for that time period.

What you see as irrelevant might give interviewers some insight and a good opening for questions. It might also give you a competitive advantage over other candidates and is unlikely to put you at a disadvantage. 

This kind of C.V. doesn’t have to be rigorous and exhaustive. Responsibilities/work experience is sometimes (usually) listed chronologically from most recent to oldest. The most recent is often the most relevant but it all paints a picture. As an interviewer, I would definitely ask for clarification on any gaps. Gaps can be seen as deceptive and might cause a C.V. rejection.