Whenever I mail the Vermont Philatelist to our members, I always send a test copy to myself. Last week (December 14, 2019) I mailed the envelope using imperf Loonie Toons stamps from the right section of the booklets they came from. The other stamps in the booklet had been used so I didn't destroy a booklet.
When I went to the post office today, the clerk told me that the postmaster wanted to see me and he handed me the test envelope with notations that the stamps were not "official" and I needed to pay 70c postage due. I told the postmaster they were official stamps and explained why they didn't have perforations. He knows that I know a lot more about the philatelic aspect of US stamps than he does. He told me not to worry about paying postage due and gave me the envelope.
This has happened to me before. A few years ago I used stamps from an imperforate press sheet to mail about 75 covers to my stamp club members from a post office in Vermont. My postmaster got a phone call from the Vermont postmaster warning him that I was using computer printed imperforate stamps to defraud the post office. Again, once I explained to my postmaster everything was fine.