Thank you, @Ander
I will play around with that and see what works. I am struggling now with conditional formatting - the equation which seemed to work until recently for some reason stopped working for some columns but works for others. I will share it if I do not find a solution.
There is another question, however. It is regarding Event Status. Now it is used as a value from lookup table. Values can be Confirmed, Negotiating, Cancelled. I did try, however, to reword some of them and noticed that if I change them in the original table, values in the other tables do not change. No conditional formatting formulas. I wonder why? Probably because it is treated like a string. Let me give you an example:
I tried to change Negotiating into Negotiate in the Event Booking Status table. And the values in the already used table book_event did not change, though the options did.
Furthermore, in the conditional formatting or any formula, it is referenced with quotation marks “”: 
And any changes in the values do not reflect here.
Is it supposed to be like that?
Thank you.