WoWInterface - Getting a frame through global

I have been away from WoW for 2 years, just started playing again and wanted to update an old addon I had made. However, I am running into a problem. I need to get each of the party frames, but the method I've used before is not working.

If I manually grab the frames:

Code:

PartyFrame.MemberFrame1

then it returns a table and I can hide/show that frame no problem.

Once I try to add it to a variable, it comes up nil. The way I've done this in the past was:

Code:

local frame = _G["PartyFrame.MemberFrame1"]

This returns nil, using just _G["PartyFrame"] does give me the PartyFrame, but I can't get the MemberFrames individually. The reason I used this method was a for loop:

Code:

for i=1, 4 do

  frame = _G["PartyFrame.MemberFrame" .. i]

end

This used to work (2 years ago) but now it's nil. Did the _G change, or am I just missing something obvious here?

Tried searching around on the internet but can't seem to find a change.