Abstract: We study stable bookshelf smectic-A structures within a very thin plane-parallel cell of thickness L in which the mismatch between surface preferred (ds) and intrinsic (d0) smectic layer thicknesses occurs. The Landau-Ginzburg approach based on a complex smectic order parameter is used. For a weak enough smectic positional anchoring strength W smectic layers adopt the modified bookshelf profile. In a thick enough cell with increasing W a lattice of edge dislocations is continuously formed at the confining surfaces and then depinned from them. The structure with dislocations is formed when the condition d0/( d0/ds - 1 ) 2 is fulfilled, where is the positional surface anchoring extrapolation length. If the cell is thin enough the dislocations formed at opposite cell plates annihilate and consequently the smectic layers adopt a locked bookshelf structure. This transition is discontinuous and takes place when d0/(L d0/ds - 1 ) 5 is realized. To observe these transitions in a cell of thickness L 1m the conditions W 10-6J/m2 and d0/ds - 1 5 . 10-4 have to be fulfilled. All the three qualitatively different structures coexist at the triple point.