DaiB mate, your post #4 more or less discounts, or casts doubt, on the explanation given to you. I have as positively and concisely as I can given you a further exlanation and reassurance about it, plus advised you of the reason you saw what you saw- the track offset procedure being applied by some flights. I didn't sign off with 'love' or 'best regards', but you asked, and you were told. You can ask what questions you like, but if you throw doubt on the answers you receive, then you must accept the answers you get! In this age of GPS, the sheer accuracy of computer navigation now leads to flights happily flying along close to each other mid-Atlantic, but always separated vertically. What you saw is actually very common.