I don't see why the collection resolver has a problem because the desired collection path: #<path:/home/don/.plt-scheme/4.2.1/collects>, is shown to be in the current-library-collection-paths:
(current-library-collection-paths)
'(#<path:/home/don/.racket/8.1/collects> #<path:/home/don/racket/collects/> #<path:/home/don/.plt-scheme/4.2.1/collects>)
Thanks
Don.