Mike,
not necessarily.
Having contributed to an article on Roberts a year or so ago I may be qualified to comment. The Roberts numbering system in some respects follows no logic - my own three Roberts road frames have three digit frame numbers and are early frames. The post 1979 numbering system switched from a 4, 5 and 6 figure system to a more consistent 6 figure one - your 4 figure number falls outside this later system.
Example, frame number 010101 was the first frame built in 2001, Chas commented that the system sometimes varied (!) when frames were earmarked for trade or for painting by a third party - this is after Roberts ceased painting in house and subbed out to Dave at Colortech. The first numbering system ran from (approx) 100 to 2100.
An image of your frame would help in the dating.
I have another (#4) Roberts - frameset and this is a 1980s one, so comparing the two might help.
Hope this helps a little.
Jon.