Sometimes, your luck is in. Let me explain.
When this kit was delivered it contained a Broad Gauge Society data sheet covering the essential details of the coach in question. Unfortunately, it was for the narrow bodied variant, but I didn't think any more of it. Most of the rest of the info was adequate for my needs.
Of course, now I come to think about the transfers I find I need some suitable running numbers. The data sheet being the wrong diagram - U21 - meant I didn't have suitable numbers. The answer is, obviously, to get the right data sheet for the U20. The BGS has a large collection of data sheets on all kinds of things, including many of the passenger vehicles I shall be expected to build. I plan to get the relevant data sheet pack, but it probably wouldn't arrive in time for me to complete the model for Telford.
While I was browsing the BGS web site data sheet page, I rolled the mouse over the thumbnail image - and lo! It turned out to be the U20 diagram!
Now I have the range of numbers I need, and information that I was missing, such as there was actually a lamp fitted over the luggage compartment.
Serendipity. You can't beat it.