Stack data from multiple delimited files into one, with variable columns

I'm new to scripting. Got struck with a file merge issue in Unix. Was looking for some direction and stumbled upon this site. I saw many great posts and replies but couldn't find a solution to my issue. Greatly appreciate any help..

I have three csv files -> Apex_10_Latest.csv, Apex_20_Latest.csv, Apex_30_Latest.csv. Number of columns are varying in these 3 files. Typically the latest file, based on the numbering, might have some new columns appended to the end. So I want to take the latest header and stack the data from all the 3 files into a new file Apex.csv. When stacking the data from older file which might have less columns than latest file, I want the data to be populated as null with appropriate delimiters..

Also this has to be done recursively for a multiple set of files (3 each), all in the same folder.
– Apex_10_Latest.csv,Apex_20_Latest.csv,Apex_30_Latest.csv – merged into Apex.csv
– Code_10_Latest.csv,Code_20_Latest.csv,Code_30_Latest.csv – merged into Code.csv
– Trans_10_Latest.csv,Trans_20_Latest.csv,Trans_30_Latest.csv – merged into Trans.csv

Following is the format of the source files and expected target file…
SOURCE FILES:

• Apex_30_Latest.csv:
  A,B,C,D
  1,2,3,4
  2,3,4,5
  3,4,5,6

• Apex_20_Latest.csv:
  A,B,C
  4,5,6
  5,6,7
  6,7,8

• Apex_10_Latest.csv:
  A,B
  7,8
  8,9
  9,10

EXPECTED TARGET FILE:

• Apex.csv
  A,B,C,D
  1,2,3,4
  2,3,4,5
  3,4,5,6
  4,5,6,,
  5,6,7,,
  6,7,8,,
  7,8,,,
  8,9,,,
  9,10,,,

Thanks…