Cheers Booth and Andygo.
In contemplation of "what could have occurred to cause some slight coolant loss?" it actually did no harm before they started the work to be able to also email them pictures of a coolant reservoir displaced and upside down in the engine bay during the timing chain tensioner replacement process, a job they recently did. Along with other things pointed out to them, it set a reasonable 'fighting my corner' scene, should that later become necessary.
It's all about trust. Due to the negative experience at a different garage in the months after the initial buying process, unfortunately it takes some doing to get that trust back.
For anyone's future reference:
If you have a warranty and coolant loss and you intend to take the car to an authorised warranty repair garage, then beforehand, take good close up photographs of the front honeycomb grille on the car being intact and undamaged (if that is the case) so that you can challenge any suggestions that stone chip damage is the cause of radiator failure, ie how likely is it that a stone would get through those small holes without also contacting/ damaging the plastic honeycomb grille surrounding the hole?
Likewise, if you can, photograph the intact and undamaged protective tray underneath the engine bay (if that is the case) to be able to further challenge the probability of a stone finding its way up to the radiator to damage it.
