Generally, they were in the 70s and 80s, when the import market was still relatively young. By the mid-90s or so, Japanese manufacturers had more or less caught up, but Toyota specifically had a few missteps around 2003-2009 where rustproofing completely failed on their truck frames. Their other models have a bit of a reputation for rotting out extremely quickly once the rust starts; I'm not sure if it's something in the composition of the alloy that they use, or what, but it was kind of eyebrow-raising to hear, given how impeccable most of their engineering is.

More recently, they've been including rust treatment under warranty, but it sounds like it's just a silicone-based coating that they spray on once and do not reapply. Either way, if you have a Toyota or Lexus and the body is showing signs of rust, get it treated ASAP. Lanolin-based treatments (e.g., Fluid Film or Woolwax) work really well, but have to be reapplied at least yearly (and you have to avoid spraying the undercarriage at car washes). Avoid POR15 like the plague; once it fails, it fails catastrophically.

...I may or may not have spent the past six weeks down a research rabbit hole because I own a Toyota that is starting to rust side-eye-1