Still question stands with those kind of situations - 3DPOLYLINES and many of them... Fortunately I did find solution : as how I generated 3DPOLYLINES from POLYGON MESH, I almost just changed command "3DPOLY" to "SPLINE" and I did get generic splines instead of 3DPOLYS... Now the problem existed still until I tried with only edges splines and middle ones that are determining curving of surface... So I picked 3 in first direction and then other 3 in second and surface was generated... Then at the end I changed SURFU and SURFV to match M, N values of polygon mesh (64x64), but as a result network don't exactly match at middle curving splines... But it did what I wanted; still I think that it should do it and for many curves along curvature of surface and it shouldn't be the issue with curve entity types - it should work and with 3DPOLYLINES as well... So solution is somewhat cumbersome... I'll attach my final DWG...
M.R.