"... The two that switches on the Walkman would pick up Read only and Type II - But why? ..."
It looks like the outer larger switch is actually a 'cassette tape inserted' detection switch rather than a write protect hole detection switch. It must be large enough to pass over the hole.
Here is a similar set-up on the WM-EX674 showing the ATS / Tape switches
The type IV metal detection ability would require another switch which is not shown however.
"...I didn't know that about the Minicassette though?..."
Neither did Stanley Kubrick by the looks of it:
"A Mini-Cassette of Beethoven’s Symphony No. 9 can be seen in the 1971 film A Clockwork Orange, but the Mini-Cassette was not used for music recordings (unlike the Microcassette)."
I know! I knew I said it wrong in the moment and couldn't get it off the tip of my tounge what I was trying to say!
I didn't know that about the Minicassette though? Wouldn't that mean a variable quality over the length of the tape as it spooled faster and the driven roll got bigger? Although I guess quality can be tuned for the human voice much more with a dictaphone?
Good point on the type material, the read only tab was the outer most, then a tab for type II next to it. Type 4 tape was much closer to the middle of the tape. The two that switches on the Walkman would pick up Read only and Type II - But why? I seem to think at this time most good HiFi sets were slot loading for casssettes? And I don't think you'd use this highly engineerd miniture mechanism if space wasn't an issue? Interesting question!
They were known as 'Compact Cassette' in the UK.
The smaller Dictaphone/answering machine cassettes being known as 'Minicassette' (Philips ?) and 'Microcassette' (Olympus ?).
I seem to recall that the Minicassette was spool driven, whereas the Microcassette was capstan driven like the Compact Cassette.
The microswitch notches on the back of the cassette were write protect on the outside, then type II chrome immediately next to it, then type IV metal much further in towards the centre of the cassette. Why it would have a write protect detect switch is a bit of a mystery unless it shared the same chassis as the recording Walkmans.
Another great tear down.