Timing belt change interval

Anyone advise me on when a timing belt on a mk1 Golf GTi should be changed? I have a sticker in the engine bay from 'Optibelt' saying a date of 26/04/15 and 168,418 miles. Would this be the mileage and date? that the cambelt was changed or should be changed? I can not find a receipt for it in my receipts file. I hope it was done by the previous owner. The car has done about 175,000 to date.  Also I have a second question. I found a receipt for a gearbox oil change in 1994. Is it safe to say it should not need changing again?

It should mean when it was last changed. 

There's various opinions on when they should be changed but as the cars are far from new, I'd change them at 40-50k.

I'd also pull the cover off every 10K and have a good look at it. 
If you do change the cam belt, replace the water pump at the same time! 

Cheers! Why is it advisable to change the water pump at same time?

its not on a mk1

volkswarren said

its not on a mk1

Strange because jazman is asking about a Mk1 Golf GTI, or at least that's what I thought I'd read above.    

If your water pump goes you have to take the belt off etc… to gain access to it, so while you're changing the belt it's advised to do the two together.

The pump won't cost an arm and a leg, that and you have piece of mind about when that was last changed!  

It's not required on a mk1 is what I ment.
If it goes on a mk1 u have to remove the fan belt, not the cam belt.
Waste of time changing every time you do a belt on a mk1 GTI.  

There is one bolt that passes through the cam belt cover that's it.

 
I understand what you mean but I've always understood that it's just best practice.  

So how often do you recommend changing the belt and how often the water pump out of interest?   

On modern engines that have the water pump driven via the cam belt it's common sense to change at every interval.  The mk1 water pump (1.5and above)  won't affect the cam belt even if it was to seize. And can be removed without touching the cam belt.
I can check my auto data book tomorrow but it's every 4 years I think. For a belt and tensioner, I'd doubt many mk1s need worry about the mileage side of the change.