I go for four perio cleanings a year. is it usual practice fora periodontist to write down any pockets over 6 mm into notes following each visit?

Not really: We generally write down every gum pocket depth (6 measurments per tooth) for every tooth on a yearly basis. I think that more than that can actually reseed infections throughout your mouth. Taking bacteria from a 6mm pocket and inoculating a 2mm pocket. Unless there is a specific problem that needs to be addressed once a year is standard.

Charting Protocol: Every general dentist or periodontist has his\her own protocol regarding periodontal charting & record keeping. It is important to monitor pocket depth and periodontal health from visit to visit so that we can advise patients on their oral hygiene & periodontal health and which areas may need more attention. We can judge this not only by probing pockets but color & tone of gums, bleeding, etc.