It’s possible that the ice was picked up in IMC between the buildups.
A good reason to keep out of IMC when there are any buildups around 
But in that case the extent of the IMC (at that level) was clearly limited in distance.
20-25 Knots, 500ft climb rate, time VMC/below 0 OAT, 5 Minutes during climb, worst icing just before the tops reached (always a bad place/point)!
5-10 Knots, only 5 Minutes CU/TCU cruise/during climb.
5 Knots, after 60 Minutes cruise IMC below 0 OAT, Stratus
I only like this PIC
Super useful thread, great idea
This famous pic which dates from some years ago
relates to this story
The impression I get is that he got this ice at FL140 or so and during the descent from there. Clearly he was unable to hold altitude at FL140 and I really don’t think a TB20 would hold altitude even at 5000ft with a deiced prop and at full power with this much ice, so he was lucky to reach an airport.
