OK so will follow up with some details of the 1989-95, or so, period. If anyone is able to fill in the gaps, feel free to do so!
The 1989 timetable has come up on a recent thread about Clapham Junction IIRC, but will discuss nonetheless. Probably the biggest change in the 80s, the Basingstoke/Alton 'dividers' finally ended, with the Alton trains running as a separate service (one Alton, one Farnham per hour as had been the case since 1985). Furthermore, the '75' Guildford stopper became a '53' to Farnham, giving Farnham three trains per hour off peak though the slow was I suspect overtaken by one of the faster services. Also the 'Greyhound' CIGs were introduced on the Portsmouth Direct, with improved journey times, and I think they skipped Woking.
Out of Waterloo it was something like this (thanks to whoever posted on the Clapham thread for refreshing my memory):
xx05 Basingstoke (Clapham, Surbiton, Woking, all)
xx15 Exeter or Salisbury
xx15 Portsmouth and Southsea stopper '73' Clapham, Wimbledon, Surbiton, all
xx20 Portsmouth semi-fast '82', Clapham, Woking, Guildford, Farncombe, Godalming, Haslemere, Liphook, Liss, Petersfield, Havant, Bedhampton, Fratton, PSS, PH
xx25 Farnham semi-fast Surbiton, Walton, Weybridge, Woking, all
xx32 Weymouth fast '91' - think it was fast to Parkway by then. 442s fully introduced by now IIRC.
xx35 Southampton Central (Clapham, Surbiton, Woking, all)
xx45 Poole '92', similar pattern to earlier but now with Clapham Junction and Pokesdown stops. Again mostly if not completely 442s by now.
xx45 Farnham stopper, Clapham, Wimbledon, Surbiton, all
xx50 Portsmouth 'Greyhound' 81 - Guildford, Haslemere, Petersfield, Havant, Fratton, PSS, PH
xx55 Alton - Clapham, Woking, all
Perhaps it was the NSE influence but interesting that in 1989 almost everything ran at exact 'divisible by 5' departure times.
Of interest that year was the variety of stock on the Southampton stopper ('93') which was 100% VEP just a few years earlier. Daytime services were a mixture of VEPs and CIGs of various lengths, including some 12-cars working up to London just before the peak - and of particular interest were about two up and two down services per day which were TCs, hauled by a 73. IIRC the up services were around 0850 and 1650 at Southampton Central.
These interworked with a separate Southampton-Wareham stopper in most hours, with some exceptions.
Moving onto 1990, the main change was the electrification of the Fareham lines, and consequently an additional xx10 to Portsmouth via Fareham (Woking, Basingstoke, Winchester, Eastleigh and all) was introduced. Generally CIGs with a few VEPs from what I could make out. I'm not sure if this interworked with the new Portsmouth-Southampton-Wareham stopper at Portsmouth Harbour that year - can anyone answer this?
Also the withdrawal of the TCs meant that the '93's lost those unusual 73-hauled services, though a nice addition was the introduction of a Southampton-Eastleigh-Southampton round trip as the '93' had about a 55 minute turnaround at Southampton Central. (It no longer interworked with the Wareham as that now came from the electrified Portsmouth line).
This was all nicely done to provide good connections with London services: IIRC this 'shuttle' was timed to connect at Eastleigh with the Portsmouth service - NSE era timetables did seem to be planned to ensure good connections to a much greater extent than recent timetables.
1991 kept the same basic pattern, but the Portsmouths via Eastleigh moved to 'Greyhound' operation and became self-contained (this MAY have also happened in 1990, but didn't study them enough to ascertain this). They also gained a Clapham stop. Main story of 1991 was the peak-hour cuts (e.g. 4 tph peak on the Direct, formerly 6, and many peak services shortened in September due to the withdrawal of the HAPs... last ever HAP journey I did was on the 1758 Waterloo-Southampton stopper sometime in the first week of July 1991 which was an unusual VEP-HAP-VEP 'sandwich').
Next few years are a bit more vague but I think it was 1992 when the Portsmouth fasts largely became 442 operated, presumably the recession meant that there was less need for 10.442 off peak on the SWML so the displaced units were used on the Direct. Also in 1992 the long-standing '73' became a Guildford-Portsmouth 'shuttle', with the Waterloo-Guildford '75' now running again, half-hourly, with 455s.
I do remember 1993 producing drastic cuts on the Portsmouth Direct, with just two trains an hour off-peak: looking at this thread as a whole, this appears to have been the worst service since before 1967. The '82' gained stops at Milford, Witley and Rowlands Castle and the Guildford-Portsmouth 'shuttle' disappeared. Stock was, IIRC, 442s on the '81's and CIG/BEP/CIG combinations on the '82's. Also I think the Waterloo times swapped again so the xx20 was the 81 and the xx50 the 82.
Lastly in this era, I distinctly remember a quirky Haslemere-Waterloo via Cobham service (headcode 74, run with VEPs) which ran every hour off-peak during the day. Was fast to Guildford then all to Haslemere. In one direction (can't remember which) it was looped at Guildford to allow the fast to overtake - even though it was non-stop to/from Waterloo! This was run in addition to the 1993 timetable above, restoring 3 trains an hour to Haslemere at least. I think this was in 1994/95 but I am not sure - anyone else remember this?
That's enough for now, will follow up with a 1997-2003 (slam-door era SWT) post at some point.