Well, that didn't pan out well. Last night I received a prompt to download a later version of Cornish Mainland and Branches. After completing and installing this purported update, I found I was missing the sessions that shipped with the previous version.
Additionally, Content Manager now shows many assets as 'Not installed - Payware (Not active)' and 'Out of date' for Cornish Mainline and Sebino Lake (all the sessions, e.g.).
An Extended Database Repair and re-entry of my UID credentials did not rectify the situation.
The built-in version I now have is the old version -
<kuid2:515942:100169:11> Cornish Mainline and Branches - TRS19.
The version with all the new 2019 sessions is designated "And the Not installed, Payware (Not active)" This version is <kuid2:515942:100169:13> Cornish Mainline and Branches - TRS19.
It no longer works, though it did a day or two ago when I ran the A Trip to Falmouth session.
Still being prompted to download an older version of Sebino Lake.
The CDPs for the above Out of Dates all seem to be queued up in in Cache/Internet folder which I'm reluctant to flush, but probably will soon, as I'd rather download again than have Out of Date, inaccessible assets wasting space on my rig.
On a positive note, the Edinburgh to Dundee update loaded quickly and runs well.