When the 3rd Edition of Pans Ops first came out, back in 1986, there was provision for a level acceleration segment. It was subsequently removed, but had existed for so long that many procedures are still likely to state something along the lines of "climb to (altitude) prior to level acceleration".
It was a dreadful pain to have to build into a missed approach. Made the design length much longer, even for relatively short climbs. After building the initial missed approach segment at 2.5% to the level acceleration altitude which, in itself took a lot of fiddling when the terrain is difficult, then 6 miles of level flight, followed by subsequent climb (if necessary) to lowest holding altitude (or whatever) at 1%.
I'm glad we don't have to go thru all that malarky any more!