Picasso’s early works - up until about 1930 - generally fetch higher prices than his late work, which is much more uneven.
1- How would the sentence mean differently if it was read - . . . until about 1930 - . . . "
2- what does " is much more uneven." mean? { what I get is: " is not much more regular". am I right?
Until about 1930, up to about 1930, and up until about 1930 are essentially identical in meaning.
That’s right. I’d say “is much less regular”.
The until question has been answered. “Up to” is different only in that it has wider application - it can be used for monetary figures, for example, where up until cannot be used, because that’s only for dates or other phrases to do with time.
More uneven, in this context, sometimes means that the styles are less easy to detect or, most likely, that the quality of the work is sometimes not as good as before.
It may be that the quality of Picasso’s later works are uneven, or it may just be that the value of the works are uneven. The earlier works may be more uniformly pleasing to the general public’s eye.