Hi Dennis
I'm making a couple of assumptions here. First that the original photograph was created in the UK or that the photographer was a UK citizen (I know the photographer is unknown, but the subject matter may indicate where the image was created). And secondly, that the graphic designer who colourized the image was based in the UK. I'll try and cover what it might mean if he/she was based elsewhere, say in the USA, later on.
I think you can safely assume that the original photograph is in the public domain. When it was made (the 1880s) the law in the UK at that time said that copyright in a photograph lasted for the life of the author (the photographer) plus seven years after his death. I think it is reasonable to assume that this copyright would still have been in force at the time that the 1911 Copyright Act was passed. This Act (section 21) amended the term for photographs to be 50 years from the date they were made. This provision was retro-active and so copyright in the original photograph would have ended on 1 January 1931. Being in the public domain means that you or anybody else may make use of the photograph in any way you wish. In theory someone else can take the same black and white image, colour it and sell their version in competition to yours.
Turning now to the colourization, I think, given that you say this took many hours*, it is fair to assume that a new artistic work was created and that the graphic designer owns the new copyright. The copyright only applies to the colourization, not the underlying black and white image. This type of combination is known as a derivative work. As he was commissioned to carry out the work, and it appears that it was explicit from the outset why you wanted the work done, you almost certainly have an implicit licence to use the colourized image in the way you intended (ie as a gift and as prints to sell). The designer's subsequent email appears to widen the terms of the licence to include the web and in print. As I assume you are not intending to offer copies of the digital file for sale, I don't think you would be going outside the terms of the licence to produce prints for sale. Obviously it might be best to confirm this with the designer first, but perhaps there is a reason why you don't wish to do this. The fact that the designer has stated that yours is a non-exclusive licence means that either he could produce his own prints from his image, or he could sell another licence to someone else to do this.
So that is the situation under UK law. Pretty much the same goes for most other countries where the graphic designer might be based, although the threshold for originality will vary and in some places the colourization will not be sufficient to mean that a new artistic work has been created and so no new copyright has come into being. The trouble is that it would probably require a court to decide this, which is obviously something you wish to avoid.
On you last point, Getty are well known for taking images which are in the public domain and selling licences to use them. Technically this is not illegal as long as they are not actually claiming that the images are in copyright. It was
reported recently that Getty are offering licences to reproduce a graphic depicting the Covid19 virus even though it had been created by a US Federal Government employee and so, due to US copyright law, was free of copyright.
As for using other old photographs in the future, I can't offer any general rule of thumb, except that if a photograph was made in the UK prior to 1 January 1945, it is almost definitely in the public domain here now. If a photograph was made in the USA and published prior to 1923, it is also likely to be in the public domain**. However for other jurisdictions, the situation will vary widely and it would be safest to use the current copyright term of the lifetime of the author plus 70 years after his/her death to decide when something enters the public domain. In other words if you believe that the photographer have died before 1 January 1950, the photograph is probably now in the public domain.
* This is because the designer will have made many individual decisions about how to apply the colour and these will, to a certain extent, reflect his creative personality. This is the test the courts apply to decide if something is 'original' in the copyright sense. If he had merely used an app (such as
this one) then it is doubtful that a new copyright would have come into being since the human creativity was removed from the equation.
**There's a useful chart which helps to decode whether a US-originated work is now in the public domain
here