4580 a and b
I was under the impression that the yellow base with red movable clip/hook may have had a short tow pin.
Looking more closely at real pictures instead of only computer-generated images, I see that all 4580 are indeed long, unreinforced tow pins.
https://www.ebay.com/itm/314972993887
https://www.leboncoin.fr/ad/jeux_jouets/2974892858
31300 a and b
First of all, I had erroneously marked down an "S" for short instead of "L" for long. Both are long-necked tow pins.
It's relatively easy to find real pictures of sets having both the long, unreinforced tow pin and the long, fully-reinforced tow pin.
31300 with long, unreinforced tow pin:
http://www.peeron.com/inv/parts/31300cx3
https://www.ebay.co.uk/p/7053432934
https://www.ebay.ca/itm/176166169336
https://cdn.myonlinestore.eu/94f6360e-6b...1002134303
https://aukro.cz/lego-duplo-set-5607-opr...6960480777
https://bebefreear.click/product_details/2334662.html
https://bebefreear.click/product_details/2334682.html
https://www.worthpoint.com/worthopedia/l...1877794355
https://www.ebay.com/itm/275871019394
https://www.duplarna.cz/lego-duplo-2937-...csVwhVbV2u
https://www.mimibazar.cz/inzerat/8006579...-auto-2937
31300 with long, fully-reinforced tow pin
https://www.youtube.com/watch?v=KTa8eiXqAU0
https://www.ricardo.ch/de/a/lego-duplo-5...275364244/
https://www.ebay.de/itm/353245796876
However, I discovered e.g. that black had replaced yellow in some sets. I also found that Rebrickable lists 31300 as an alternate for 31507 and 31507 as an alternate for 31300. I also found sets having 31507 of both types. This suggests that BrickLink, Rebrickable, Peeron, Brickset, etc have it wrong. Perhaps one of the two was first with a long, unreinforced tow pin and this was later replaced with the other, perhaps differing schedules for different colors/geografic markets, etc.
The only difference between 31300 and 31507 seems to be the tow pin reinforcement. To conclude;
All 31300 with reinforced tow pins were actually 31507.
All 31507 with unreinforced tow pins were actually 31300.
If reality follows these assumptions, then the variant space became a lot smaller.
I was under the impression that the yellow base with red movable clip/hook may have had a short tow pin.
Looking more closely at real pictures instead of only computer-generated images, I see that all 4580 are indeed long, unreinforced tow pins.
https://www.ebay.com/itm/314972993887
https://www.leboncoin.fr/ad/jeux_jouets/2974892858
31300 a and b
First of all, I had erroneously marked down an "S" for short instead of "L" for long. Both are long-necked tow pins.
It's relatively easy to find real pictures of sets having both the long, unreinforced tow pin and the long, fully-reinforced tow pin.
31300 with long, unreinforced tow pin:
http://www.peeron.com/inv/parts/31300cx3
https://www.ebay.co.uk/p/7053432934
https://www.ebay.ca/itm/176166169336
https://cdn.myonlinestore.eu/94f6360e-6b...1002134303
https://aukro.cz/lego-duplo-set-5607-opr...6960480777
https://bebefreear.click/product_details/2334662.html
https://bebefreear.click/product_details/2334682.html
https://www.worthpoint.com/worthopedia/l...1877794355
https://www.ebay.com/itm/275871019394
https://www.duplarna.cz/lego-duplo-2937-...csVwhVbV2u
https://www.mimibazar.cz/inzerat/8006579...-auto-2937
31300 with long, fully-reinforced tow pin
https://www.youtube.com/watch?v=KTa8eiXqAU0
https://www.ricardo.ch/de/a/lego-duplo-5...275364244/
https://www.ebay.de/itm/353245796876
However, I discovered e.g. that black had replaced yellow in some sets. I also found that Rebrickable lists 31300 as an alternate for 31507 and 31507 as an alternate for 31300. I also found sets having 31507 of both types. This suggests that BrickLink, Rebrickable, Peeron, Brickset, etc have it wrong. Perhaps one of the two was first with a long, unreinforced tow pin and this was later replaced with the other, perhaps differing schedules for different colors/geografic markets, etc.
The only difference between 31300 and 31507 seems to be the tow pin reinforcement. To conclude;
All 31300 with reinforced tow pins were actually 31507.
All 31507 with unreinforced tow pins were actually 31300.
If reality follows these assumptions, then the variant space became a lot smaller.