Anecdotal evidence
Software doesn't just magically appear. There are betas, pilots, and so forth.
I worked at ICL from 1995 to 1998. I was at the FCY03 building in Footscray, Sidcup. It was a three floor building with many outsourced support helpdesks in it. The flagship client was Microsoft, but there were many others - Escom, Seagate, Compaq, Polaroid, Motorola, Apple, just to name a few. (Actually if I recall correctly Apple were in FCY02, but many of their systems were hosted in FCY03 as 02 was a tiny outhouse of a building by comparison.)
I recall that in 1998 a small helpdesk for the Post Office was set up. It was on the ground floor, near the front of the building, at least to start with. I think it was intended to be around three to six people, quite small by our normal standards.
I'm sure I was told that it would expand as we were going to be supporting a new system for post office branches. I don't recall it ever arriving whilst I was there, and I think that when I left ICL that helpdesk was mostly supporting the Post Office's Post Code Database software. But there was a constant rumour that this tiny helpdesk would expand "soon" as they were just about to start rolling out this new system to post offices.
Aaaaaany day now. Any day. No, really, it could be any day now. Honest.
The reason this sticks in my mind is that there wasn't much more space on the ground floor. If they were going to grow that team, they'd probably have to move it to another floor. Maybe even another building. Which would mean not just repatching network ports but possibly also running new connections between floors or buildings, and all the hassle that can entail.
Around mid 1998 this ceased to be my concern as I moved on to pastures new.
But it wouldn't surprise me if there were some earlier cases than 1999. My recollection is that they were definitely saying they'd be supporting it. Any day now... so there were wheels moving in 1998, and someone may well have been using it in a pilot somewhere...