It looks like it has held up physically, but I wouldn't trust it to have held up chemically, especially if it was or will be used to hold hot liquids, which can cause plastic leaching. There are plastic products that were in use for years (if not decades) the FDA later banned or warned against after long term testing indicated they were associated with endocrine disruption and birth defects, cancer, and changes in insulin resistance, reproduction system, cardiovascular and brain function. Without knowing which plastic product was used in the thermos it would be too much of a risk for me.

As a side note, there are currently thousands of chemicals in production that the FDA has not had a chance to test, but are still allowed to be produced, which is why my personal BIFL lists tend to feature known and proven substances (glass, certain metals, cotton, linen, etc.).

Edit: typos