Doh! It's Scotland. There's no Keeper liability (for now) in Scotland. As the Keeper, you are under no legal obligation to identify the driver to an unregulated private parking company.
Do you reside in Scotland? As the alleged contravention took place in Scotland, if they wanted to take you to court over the alleged debt, they would have to file a claim in the Scottish courts. They will not do this as there is no money in it for them even if they were to win.
You can safely ignore anything and everything from DCBL. They are powerless debt collectors. Never ever communicate with a useless debt collector.
If/when you ever receive another PCN in Scotland, either ignore completely or simply respond as the keeper and tell them to bog off. It couldn't be simpler north of the English border.
For now, just ignore everything unless they somehow enter an alternate universe and issue a claim in the simple procedure. High unlikely as the £70 debt collection fee would still likely be disallowed or significantly reduced, as Scottish courts generally view such additional charges as disproportionate, especially for low-value claims.
The £100 PCN would remain the core claim amount. Since the claim is under £300, no additional court expenses or solicitor fees would be awarded, as per the rules of the simple procedure in Scotland. This means VARS would not be able to recover any court fees or other costs beyond the original PCN amount. It simply wouldn't be worth their while for a single PCN.
So, ignore everything unless you ever receive a court claim, which would mean you have entered an alternate universe and then come back here for advice.