B is the indicator that your Peugeot was manufactured in Beaulieu, the older of Peugeot's facilities. It's the facility where Peugeot had their Prestige frame shop that manufactured the team bicycles and custom frames. However, they also did semi-mass production, hand-brazed models and the mass production, machine brazed models.

I'm assuming the lead character on the blue frame is poorly struck 'B' as opposed to a '3' or '8', as it's offset from the other characters. However, like the black frame, I'd advise checking under the under the cable guide for other characters. It could completely change the apparent year.