I expect John and others could fill in the blanks on this, and maybe add some more (such as new engines). . .
- RPO/date of first production S1 saloon

- date of Press launch of the cars
Official launch date France May 23rd 1989 (source XM 0 No.1)
Official launch date UK October 28th 1989 (source XM 0 No.4)
- RPO/date of first S1 estate
New Vehicle Document dated 28th February 1992 (source XM 0 No. 14)
- RPO/date of start of Hydractive II
5929 / 1 Feb 1993
- RPO/date of first S2

- RPO/date of last XM off production line

Total XM production for the 11-year run is stated as 333,775 (Wikipedia) and 333,405 (table below).
For the year MY 2000, the table lists 714 petrol cars, and 1632 diesels, 2346 in total.
.
Above table more legible: * Link to our Members' Register of XMs: viewtopic.php?f=19&t=7089#p81829