Exactly! Czech and Slovaks are great friends. Languages are basically very same. Problems or more likely issues with one nation were the same for second nation as well even during joining EU. But Uk/Scotland..Spain...? But there are always conditions....

But look at UK/Scotland. Let´s say Scotland 2014 referendum got them independence. Sure there would still be question about the potential Brexit (around now ) but we can assume UK would be still part of EU as of now plus maybe little longer because firstly UK/Scotland would need to settle thing between them. In such situation UK and Spain could easily block any attempt to join EU for Scotland. Spain for fear of independence for Catalonia, Basque and UK for whatever reason...let´s say in case the Scotland independence was not completely nice process. It is basically another bargaining chip for UK in independence vs EU membership.

But now? UK is leaving. So by this UK will lost any control over if Scotland can or cannot join EU. Plus whole Brexit is somewhat damaging EU public PR as member is leaving project...so there will be political will to counter this. Best way is getting new member. New old member is especially great as you don´t have to add some states which are not quite "there yet" (Turkey?). Political will to repair public EU PR easily counters whole Spain especially if Scotland will leave in very legal way. States have control over legal process. You can fight windmills forever...So Scotland legally leaving UK has is giving no special room to Catalania and others.

Still current issue is future of UK. There might be yet another crisis in next years, brexit at its own, trade deals take time. Short question, will UK see new golden age soon after brexit or not? If not and there are major (economical) issues, it will bring probably the biggest opportunity for independent Scotland. And Unified Ireland. Because logic is simple, golden age for UK = nobody wants to leave UK. Crappy age for UK = somebody gets idea that leaving might be option. And then of course right back to EU..