The "ROM list" for 0.139u1 refers to the specific collection of game files (ROMs) that are compatible with this exact version of the emulator. In MAME, ROM sets are version-specific; because the MAME team constantly updates how hardware is emulated to improve accuracy, a ROM that works in version 0.78 might not work in 0.139, and vice versa. Key Characteristics of the 0.139u1 Set Game Count : This set supports approximately 8,000 to 11,000
If you're looking for a list of ROMs compatible with MAME 0.139u1, here's what you can do: mame 0139u1 roms list
If you are compiling your own ROM list, you must note that emulation improved or broke specific protection schemes in this version: The "ROM list" for 0