I also have a late 2000 LS430 and live within the CC and ULE zones.
My late 2000 LS430 came up as NOT exempt from ULEZ, despite 2001 onwards LS430s are ULEZ exempt. I was gutted and most reluctant to make such car redundant due to some stupid charge, I started to google.
Although built in the era of EURO 3, the LS430 was an early adopter (TFL term) and exceeds EURO 4 standards (even EURO 5 compliant on CO, HC and NOx, although the CoC did not show PM values):
Euro 4 emission limits (petrol) LS430
CO – 1.0 g/km 0.230 g/km
HC – 0.10 g/km 0.040 g/km
NOx – 0.08 g/km 0.020 g/km
PM – N/A for petrol
source: http://www.emissionsfinder.com/lexus-all-models-ls430-43cc
https://blog.lexus.co.uk/innovations-of-the-third-generation-lexus-ls/
As all the LS430 had the same 3UZ-FE engine, and since the MoT emission requirement for 2000-2006 LS430s were identical, I wondered if there was any difference in emission pre/post 2001.
I researched and contacted Lexus, they were not able to confirm/deny in email communications any difference between pre and post 2001 LS430s.
Initially Lexus emailed an EURO Emission Letter stating the obvious, EURO 3 compliant (as the car was built under this regime).
I went on to press for the detailed emission figures, Lexus then sent me a duplicate Certificate of Conformity, which confirmed 2000 LS430 has the above emission figures, same as post 2001 LS.
(without asking me for the £75, but probably because I bought my LS430 from Lexus dealer and I was not given the CoC at the time).
I just made an application to TFL with the CoC and V5, will see if they grant the ULEZ exemption.