Just to add a couple of things to what John has already correctly pointed out,as there are no 'straightforward' answers to your questions...the whole subject of 'transition liveries' being something of a minefield
,so you need to study plenty of photographs to get an accurate picture.
Rail Blue was generally applied from 1966,but some early repaints had small yellow panels [SYP from hereon] before the full yellow end [FYE from hereon] was finally decided upon.
Some early Western Region 1966/7 repaints used a 'Chromatic Blue' [slightly metallic finish] with SYP on some Diesel Hydraulics.
The JB version of the Cl.73's were delivered from new,in 1965, in Blue/SYP livery,the first 7 having a light grey band on the bottom of the bodyside.
Some locos only had their green livery touched up when getting FYE.Application of FYE starting late '66/early '67,varying with the regions,and sometimes done at the depot without the loco having a works visit.
SYP started appearing on diesels/multiple units from 1962,although it took a while for it to be applied to some...
The Southern,for instance didn't start applying SYP until relatively late in the day,the first JA type Cl.73 no E6001 having it from new[1962], but the next 5 JA's not having it untill applied much later [1967 it seems]. Class 33's [apart from D6530 which was the first and had a larger SYP than the others with rounded corners on the top] didn't get SYP's applied until the summer of 1966,and I'm sure that a few of them never recieved it before being painted in Blue/FYE.
Then there was the 'experimental wraparound FYE' that was applied in mid 1967 to a handful of locos and units from most regions on either blue or green livery [as demonstrated by Hornby's incorrect application of this to a Cl.121 unit]
Obviously this is only a brief description of the variety to be seen,but it hopefully gives a bit of an idea on this vast,and fascinating subject.
There is no substitute for thorough research,and if modelling a particular subject,work from a photograph of it taken at the time....
As a contrast to this,however, the application af TOPS numbers seems to have been fairly swift in late'73/early'74....even on stuff still in green...