Miss SaigonPrince Edward Theatre, LondonThe Pajama GameShaftesbury Theatre, London Some theatrical productions are budgeted and publicised with the expectation of being a hit, while others sneak up on success. An example of each is provided by two just-opened West End musicals: the Miss Saigon revival seems to have been advertised on the side of London buses for at least a year, while the new production of The Pajama Game has been rewarded with an unexpected transfer after audiences and critics were surprised by its charms at the Chichester Theatre last year.And expectation turns out to be the only real problem for Miss Saigon. Because 25 years have passed since the first production opened – and 15 since it closed – there will be generations of theatregoers who come to it fre