The VPAF had periods where they didn't go up - this seems to be after the current tactics they were using failed in a big way - they then changed tactics and started again.
There is a Hungarian Istvan Toperczer who has had access to the VPAFs files of that period and he has produced a couple of books based on this research.
He quotes that the end of 67 and Feb 1968 were busy for attacks on bases - though at the end of 72 the airfields were being Hit nearly every day however MiG operations still continued in a limited way despite being suppressed. They moved the jets around country - had a lot of airbases and a lot of chinese / NK engineers and locals to help repair the airfields. Also China was right next door and had safe haven airfields there - which is where they had to move training to in 72. there are no records for how many MiGs survived LBII he says. They
possibly had over 200 MiG-21/19/17s at the start of 72 (not confirmed).
MiG-19 combat operations ceased in Aug 72 due to combat losses and attrition - so should only be in Linebacker 1