Yeah, the seventh tone in Guangzhou Cantonese that’s gone in Hong Kong Cantonese is the high-falling tone.

In Guangzhou Cantonese, 衫 (shirt) and 三 (three) are not homophones, but they are in Hong Kong Cantonese. The Jyutping romanization (from the Linguistic Society of Hong Kong) reflects this change in HK Cantonese (saam1), whereas Yale, based on the older pronunciation, could represent the difference in tone (sāam vs sàam).

Interestingly enough, the high-falling tone is still retained in Hong Kong Cantonese for one exceedingly common word, the final particle 㖭 (tim1/tìm)!