Underexposing a negative will always result in loss of shadow detail. Push processing, special developers, and intensifiers cannot bring out any detail that is not already there. Fast films and pushing are only two things that are used in dim light situtations. It is always instructive to look at photographs taken decades ago without the benefit of fast films available today. How did they obtain the photo?
It is unfortunate that Ilford chose to call it 3200 implying falsely that it is a true ISO 3200 film. The following is a quote from Ilford's website, "DELTA 3200 Professional has an ISO speed rating of ISO 1000/31º (1000ASA, 31DIN) to daylight." Exposing it at EI 12500 which is almost 4 stops under will result in a near complete loss of shadow detail. Ilford goes on to imply that exposing it above EI 6400 is not recommended.