This notation represents a date range indicating a period of time that began in 1952 and ended in a year in the 1900s, the exact date of which is unknown. The "19??" portion signifies uncertainty regarding the specific year of termination. This format is commonly used in biographical entries, historical records, or other contexts where a start date is known, but the end date is not precisely documented.
The double question marks "??", often used together, serve as a placeholder for the missing two digits of the year. This is a widely accepted convention across different fields of study to denote incomplete or unavailable date information. The implication is that the year ended within the range of 1900 to 1999.
When encountering this notation, it is important to acknowledge the inherent uncertainty and avoid making definitive claims about the period's duration or end date. Further research or corroborating evidence may be necessary to establish a more precise timeframe. The notation itself signals a recognized gap in the available data.