Need Help Reading Scott Catalog

I am having difficulty understanding some of the entries in Scott.
As an example, consider Russia catalog numbers 73-87. The heading in Scott reads "1909-12 Unwmk. Perf. 14x14-1/2 Wove Paper"

The listing for number 73 reads "73 A14 1k dull orange yellow"
The listing for number 73a reads "73a 1k orange yellow ('09)"

If 73a was issued in 1909, then when was 73 issued? 1909 or 1912?

Confusing this further, 77a is identified as "('12) and is the only one so identified.

In this group of issues, 12 of the a's are identified as ('09), two are identified as ('10), one as ('12) and 84b as ('09).

How do I interpret Scott for the date of issue for the primary issues, 73, 74, 75, 76, etc? ('09) or ('12)?

Many thanks for your help.

Donald

In scott All the stamps on the first line are 1909.Color varieties are given with their respective dates.If the date (09) is the same for the variety that's because it was also printed in that year.If the variety was (10,12) that was the year it was printed.
In fact their are many varieties: check this cat. for detailed info..

http://skandinav.eu/page18.htm

Merci bien. Je comprends.

Donald

Perf 12

Thanks for the link. Added it to my favorites. Those stamps have been a source of great confusion for me.