I highly doubt that there were a many SXS switches "though the LERG isn't always updated when a switch is replaced."
I took a look at an early 2003 LERG, and yes, there are still CLLIs with SXS for equipment type, listed in LERG7 (that section is the "inventory" of switches, default-sorted by LATA, also indicating an abbreviation for equipment type). But those listed CLLIs with SXS also had a corresponding CLLI entered right after or right before, for that same location (ratecenter) and ILEC, with a digital (remote) equipment type. The CLLI itself was of a form indicating digital or remote.
What happened is that the ILEC or their agent entered the new CLLI for the new digital or remote switch replacing the SXS switch, in LERG7... but the ILEC or their AOCN agent never got around to removing the older SXS switch/CLLI from LERG7. An entry of a distinct CLLI in LERG7 is necessary before one can reference that CLLI in LERG6 (t section of the LERG listing NPA-NXX office codes and associated data), LERG7SHA (switch homing arrangements), LERG9 (Tandem homing arrangements), and other related LERG sections or files.
I think that since then, Telcordia has made several quality edits to their BIRRDS database to prevent old data from remaining in LERG7 (the switch inventory) if that switch (CLLI) has NO corresponding associated data or reference in any other LERG files (sections) such as LERG6, LERG7SHA, LERG9, etc. But years ago, Telcordia had to "manually" run individual data reports each and every month to find "old hanging data" of extinct switches still appearing in LERG7 if that switch had no such related, referenced data in ther parts of the LERG. That monthly report was known as the "Dead Switch Society" report, and was emailed to "offending switch holders" for them to justify a reason for retaining such extinct switch data if it didn't appear in other reports of the LERG.
BTW, it wasn't just ILECs and SXS or #5XB or old and now replaced 1AESS. CLECs which no longer exist might have their old switches/CLLIs still listed in LERG7, but these no longer exist in real life. Hopefully, the NPA-NXX office codes in LERG6 that the CLEC had have now either been removed altogether, or else corrected with the new telco and switch.
So, for MOST of those remaining SXS switch CLLIs in LERG7 in 1999-2002, cross-reference that CLLI and see if it is associated with any NPA-NXX office code in LERG6.
As I mentioned in my earlier post in this thread (and I too renamed it since "How's Pat" isn't applicable -- my renamed post is "Switching History"), Nantes in Quebec is believed to be the VERY LAST SXS switch in the North American Dial Network, cutover to a Nortel DMS-10 in June 2002. I can't speak for any remaining legacy SXS switches in the PUBLIC telephone network (as opposed to PBXes, museums, private collector networks connected by VoIP, etc), in parts of the world outside of Country Code +1.
- a/b