documentation/references: 全 being pronunced `qian` in Southwestern Mandarin I'd always had this hunch! The bus recording was supposed to be 安全 but why did it sound like 安前.
Then I got affirmation from 《成都方言》


刘前进
此词源于《刘全进瓜》的古典故事，即与瓜傻同义，便指傻瓜。又由于地域读音关系，“前”与“全”不分，此词又为“刘全进”。歇后语：“～——瓜！”

Specifically: “前”与“全”不分.
This, though, is the only evidence or documentation/reference I have come across talking about this phenomenon.
What other references or documentation exist talking about “前”与“全”不分 or 全 being pronounced qian in Southwestern Mandarin, or more specifically Sichuanese/Chengduese?
I am working in Chengdu. But I don't think they don't really 前/全 不分, they can easily speak 全 though maybe sounds a little different on tone with 普通话. Maybe the pure ancient 四川话 has the difference as you talked. But nowadays, it's not so obvious. Maybe caused by the develop and immigrants from other place, the 四川话 also changed day after day. 所以，如果如今的四川话和过去的不太像了，你也不必感到奇怪。