Well, it looks like Sony has given up designing or at least programming their own remotes... this feels more like a UEI implementation with all the stupid 3-digit setup codes (up to and including the previous RM-VL610 Sony was far more intuitive in operation).
At any rate, I have managed to get my sample to learn without issue.
1) Press SET for 3 seconds. - after 3 second the SET light will come on.
2) While continuing to hold SET (don't release it), press the OK button. - the SET light will now stay on when you release both keys. - you cannot simply press SET and OK for 3 seconds, it has to be SET by itself and THEN add OK.
3) Press 9-8-8. - the SET LED will blink on each number entered. - after the third number the SET LED will blink 3 times. - if you enter something wrong the SET LED will simply go out.
4) Press the device key to learn a button on. - both the SET LED and device LED will remain lit.
5) Press the target button to learn on. - the SET LED will blink once as you push the target key, but nothing else will appear to happen. - it is not necessary to erase a button before relearning it.
6) Aim the source remote at the front of the RM-VLZ620 and press and HOLD the original source button until the SET LED blinks 3 times. - if the set LED blinks once the code was NOT captured. It must blink 3 times. - after a command is learned the device LED will go out, but the SET LED will remain on. - if you fail to send a signal in time, both LEDs will simply go out and you'll have to start over.
7) To learn another button, repeat steps 4 through 6.
The timeout is VERY short on this remote, so if the SET LED ever goes out you will have to start over at step #1.