Well, jbholio figured out a while back that there were possibly two batches released of games (with slight differences in-game), and I think I can definitely confirm that with a 2nd copy of El Monstruo de los Globos (Balloon Monster) that I purchased recently.  I haven't compared the gameplay yet as my converters are stored away, but here are some exterior and pcb differences:

1st release:
Main label missing a bunch of text (which all my other gluk carts have, so this must be a real early release?)
Original CN-05 label underneath Gluk Video label.
Bulky short black screws (when opened up you can tell that they are not perfect fit for the case)

PCB:
Actual (windowed??) EPROMS, and you can tell that the board is much older

2nd release:
Main label has extra text
No original label underneath
2x Thin and long 1x short silver screws (perfect fit for the case)

PCB:
Cheap board with no EPROMS...not sure what they're called, those two black spots of solid that looks like liquid...board also looks almost brand new

I don't know how far apart these were released, but given the different type of boards...I think a number of years.  My guess is that Gluk Video released them originally in the early 1990's when MegaSoft/Caltron was producing these games, and then later rereleased them with cheaper PCB etc. 

I'm gonna look for a converter in a bit and test them later today....curious to see which differences there are.

EDIT:  Here is the info/numbers from the PCBs, incase anybody knows what any of this means (Michael ):

1st release:

black thing on top:  KC5373B-010
PCB: N715061

Left:  mitsubishi sign??  M5L27256K  -2
827108
Japan

Right:  Panasonic
MN27C64A
-15 FA

FGT7216
9014VE


2nd release:

black thing on top:  KC5373B-010
PCB:  N715062      VCC

Thanks for the extra stuff! 

That's pretty cool that you were able to find those two versions with totally seperate circuit boards and everything!

The back splotches where you are used to seeing chips are called glop tops.  They're the roms and stuff without the plastic shell and then covered in resin to protect it.  It's cheaper than normal rom chips.  They're pretty common in pirates and earlier famicom games.  As for nes, about half of the super mario/duck hunts use glop tops.