10c Fisher Envelopes Of 1976 - Questions

Can anyone help with a question or two about the 10 cent Fischer design envelopes issued in 1976. Both sizes were issued in two types. One with "CODE" printed on the front and a request to use the post code on the back. The other was without this additional printing.

The examples I have of the plain envelopes are constructed from a bright fluorescent white paper stock while the "CODE" envelopes are on a non-fluorecent paper stock.

Is this always the case ?

Also what was the date of issue of these two types and were they both issued over the whole of the country.

If the issue dates are not known then is it known which type was issued first?

AQ

Unitrade does not give any additional information other than that they were issued 1975-79. No mention of paper type either.

Thanks for that. I did know that and would add Webb issue 7 has no more information either.

Considering all the interest in the fluorescent grades of the stamps issue at this time I find the lack of info rather surprising.

Two different papers were also used for the two types of size #10 17c Fisher envelopes issued in 1979. There are probably more variations as well on other issues.

AQ