Citing microfilm derivatives from the Louisiana State Archives' "Statewide Death Records" series

I'm very thankful Louisiana has the "Statewide Death Records" series for death certificates over 50 years old, however citing the source has been tricky to me.

 When you use the Louisiana Death Records Index online (http://www.sos.la.gov/tabid/640/Default.aspx) to find an entry, you can select an option to fill out a form with your mailing address and then have a PDF order form produced, which is pre-populated with the relevant details needed to order a copy of the death certificate.  It will have the person's name, year of death, volume, page number, and parish of death (plus the mailing address information you provided). The website notes, though, that copies are made from microfilm: "This service only issues certified copies of microfilmed death certificates for deaths that occurred in Louisiana between 1911–1961." I tried to find out if they had a catalog that shares the microfilm numbers, but they did not online.  I called the facility, and asked about how to cite their microfilm, and a nice woman told me she had never been asked that in 14 years there.  :)  She did say the films are named with the year, each  parishes is a "volume", and the "page number" is the record number. She said that every 50 years, the parishes send in the death records for the new year being made available, and are then filmed.  She said the volume numbers rarely change, just year, and the numbers start over at "1". That being said, how should we cite the records they provide, since they are derivatives of microfilmed originals?  I looked at the vital records register format, which seems to work re: "year: volume no. number, first_name last_name", since the actual certificate number on the copies seem to match the "page number" assigned it for their films and index database.  Yet it is still not evident they are microfilm derivatives... I appreciate any advice offered.  I am trying to not get bogged down too much in the mire.  I have wanted to properly source and cite all of my research for a long time, but this has been what I dreaded.  :) Thanks again!Jenny