I can contribute with two serial-numbers, I recently bought a
Miki Sakai bike, branded Fåglum! It has a Miki Sakai-sticker and the serial-number
M2C07685, which would make it a 1982. Dura Ace AX seatpost, steer and breaks. Gears and crankset are 600AX.
Gösta and Erik Fåglum, two out of the four brothers that dominated the Swedish cycling in the 1960's and 70's, supposedly put the wheels of the bike together. One of the brothers was a front-figure of some kind of the
Mizutani-bikes (it was earlier called Seraph) in Sweden, for a short while. I read somewhere that he also ran a shop selling branded bikes but my clues kind of end there.
I can't add images in this post since I haven't posted ten times yet, but they are in the gallery bikeforums(dot)net/g/album/15021556
Any clues around this frame would be of great interest to me!
I also have my modified
Koga Miyata RoadSpeed where the headbadge only says 'Miyata'. Serialnumber
F510237, making it a 1977. I could find it in the 1978 catalogue. Any info on this frame is of course also welcome, even if it's not as big of an enigma to me as the Fåglum one. 
Also,
Thank you T-Mar! I have learnt so much by reading your posts and replies over the years and it has inspired me to find out even more about my bikes. Internet wouldn't be the same without you