A Frustrating Day

I had some orders today for A3 Prints of images in the Pennine Horizons Digital Archive.   Most of the images are of very good quality, but some are ok to A4 but not so good at A3.  
These tend to be photographs taken in the 1950's and 1960's by 'ordinary' people with 'ordinary' cameras.  The content is often very interesting, but the quality of the photographs not so good.
The frustrating bit is when you know you have software that can improve the printed image but, if you use it, you then encroach on the photograph's authenticity.  Very frustrating.
I just tidy up dust and scratches and any obvious damage - all this is done in Adobe Lightroom so that the actual original image remains exactly as it - warts and all.