Undated Cds, 1971 Strike?

I picked this cover up on ebay and there is a pencil marking on it that says that it is from the "Postal Strike of 1971; no date". The CDS does not bear a date at all, day, hour or year.

I can't say that I recall a GB postmark without a date and none of my sources at home are helping me and was hoping to get some help here.

I know some offices were open during the strike, but I cannot image that an office in SW16 would have been open and the slogan on the postmark was machine, wasn't it? They wouldn't have been running the machines during the strike, would they?

The location of the addressee also looks odd. Center top of the cover? The franking I got [(2d+2d)=1.5p + 1/2p=2p therefore 0.5p shortage for 2nd class plus additional 0.5p penalty for the 1p postage due.]

Some help here would be appreciated.

thanks,

Larry