I only found out because I use dd 1000's of times each day and have had to prototype some really esoteric data pipelines using it. I have even compiled a few custom versions to do various tasks.
One other nuggets of wisdom which is very poorly documented in the man page: if you have a long running dd process (I often have 12+ hr dd processes reading 10+TB tapes) you can send a USR1 signal to check the progress. Very useful to check if your tape drive has had a hardware failure.
Information on both this and the byte counts are in my man page (GNU coreutils 8.30 on Linux Mint 20) around lines 130.
Edit: I just found this in the coreutils 9.0 changelog:
dd now counts bytes instead of blocks if a block count ends in "B".
For example, 'dd count=100KiB' now copies 100 KiB of data, not
102,400 blocks of data. The flags count_bytes, skip_bytes and
seek_bytes are therefore obsolescent and are no longer documented,
though they still work.
One other nuggets of wisdom which is very poorly documented in the man page: if you have a long running dd process (I often have 12+ hr dd processes reading 10+TB tapes) you can send a USR1 signal to check the progress. Very useful to check if your tape drive has had a hardware failure.
Information on both this and the byte counts are in my man page (GNU coreutils 8.30 on Linux Mint 20) around lines 130.