Thanks for your intrest, there have been several threads on this board about this subject. Pam G. posted some great info and research on the subject, although I do not know how to repost her thread.
You could roughly date matchcovers from NV by this....

4 digit #'s or less- 1940's > early 1950's
Alpha Numeric #'s- early/mid 1950's > early 1960's
7 digit #'s- mid/late 1960's > very early 1970's
7 digit w/area code- early 1970's then by the mid 1970's the 1-800 #'s along with the 7 digit #'s start to appear
then by the mid 1980's direct nation wide 1-800 #'s are the norm.

Also keep in mind that as with todays tech. advances back then often took time for these new inovations in communications tech. to reach different parts of certain regions or cities in NV..

If you are interested in collecting mathces I have hundreds of duplicates, flattened and full books for trade or sale. I love chips but the mathces are a great way to capture pieces of gaming history. Eric