Need to convert Pantone colours to CMYK, but when trying to it will only let me have LAB colour

Are the Pantone libraries in InDesign up to date? 

I've seen the same plates on different printing presses side by side produce different shades of the same colours.

At least if I say it's Pantone 123 in the book and I used the CMYK approximation they have something to match to. 

Otherwise, as you say, it's a crapshoot anyway you look at it. 

If you do the conversion to CMYK yourself you're not doing any favours.

If you leave it to a RIPs CLUT then it might be different to what you can approximate on your side.

Without a printed proof you're not going anywhere fast. 

My method has worked well for me in the past. 

Pantone 021 C for example
The CMYK version of that is appallingly not close at all.

Yet, I've had to have the same document setup for 2 different print scenarios

Spot printing and CMYK printing

as the file was used for different processes and things.

And it was matter of mapping one colour to the other for differet scenarios

As the conversion to CMYK for the 021C was horrendous

It took some colour testing and printing with the printers.

But we eventually ended up with sets that we could send to different print vendors to match.

Nothing is easy.

And Rob Day will come along and scald me any moment. 

{braces oneself}

If you know you will never output as spot inks you might want to use the Pantone Color Bridge colors instead (they're Pantone's packaged process conversions) but how close a match you will get is, I think, somewhat more dependent on the output profile of the printing device than letting InDesign use the Lab values to find the correct simulation for a specified profile.

Keep in mind that you will never get a perfect color match converting spot color to process. Some colors convert well, others are well outsice the CMYK color gamut.