Wrexham Reserves used to play in the Cheshire League in the 50s and 60s along with other reserve teams like
Chester, Crewe, Stockport County, Tranmere Rovers etc. playing Altrincham, Macclesfield, Northwich Victoria, Witton Albion, Hyde United during that era. Reserve teams then included some good part time professionals or even amateurs.
Wrexham A and in some seasons a Wrexham B team played in the Welsh National League, Wrexham area, during this period while
Chester A played in the West Cheshire League.
Nowadays both English and Welsh FAs have a pyramid system which quite rightly, rules out reserve teams.
Personally, I favour a reserve team playing arranged friendly matches against other teams in both England or Wales, closed doors or not, which would give the opportunity for players coming back from absence, fringe players or trialists.