I’ve also tried it on various Kenwood HT’s. Some you can “push” to operate way out of band, others not so much. For example I have a NX-320 450-520 band spilt radio. The PLL won’t lock below 443 when I tried out a sequence of test frequencies. It does seem, from my experience, the narrower the band spilt the better luck you have running farther outside the official range.
If a radio is available, some come in various band spilts so be VERY careful, with the 400-470 band spilt that’s perfect for Ham and GMRS. This seems to be more frequently found with the FM/Digital mode radios. Those are the ones I watch out for on my favorite auction site. Of course you can’t use digital voice on GMRS, at least not yet so you’re stuck with FM, but perfectly legal on the Ham bands.