Hw to correct HT600 S/N?

[PETNRDX]

Ok, I know over the years I have done this, and I remember seeing the posts here, but I have searched the Archives for two days, and I can't find it...
I have a few HT600's and a couple of P200's that are coming up with the "default" S/N's, even tho they are not recased.
They have the original tags, and I want to re-program the codeplug to come up with the S/N on the tag.
But using either HT600 or P200 Rss, they still come back with the default S/N.
Anybody remember how to do this?
It seems to me that it involved using P200LB Rss, but I can't recall for sure, and so far nothing is working.
My guess is I am fogetting something simple....

[Will]

The RSS does NOT read the serial number of the radio. You can enter the s/n manually when saving the 'codeplug' to disk.

[PETNRDX]

I am beginning to think I have confused the S/N issue with the MT1000's.