set-cookie overwrite condition - google-chrome

Question

I was trying to determine the exact condition when browsers overwrite existing cookies, and found this pseudocode on the cookie specs document.
https://httpwg.org/specs/rfc6265.html#storage-model
Under #storage-model at step 11
11. If the cookie store contains a cookie with the same name, domain, and path as the newly created cookie:
1. Let old-cookie be the existing cookie with the same name, domain, and path as the newly created cookie. (Notice that this algorithm maintains the invariant that there is at most one such cookie.)
2. If the newly created cookie was received from a "non-HTTP" API and the old-cookie's http-only-flag is set, abort these steps and ignore the newly created cookie entirely.
3. Update the creation-time of the newly created cookie to match the creation-time of the old-cookie.
4. Remove the old-cookie from the cookie store.
12. Insert the newly created cookie into the cookie store.
If my understanding is correct, browsers should treat cookies with blank Domain attribute as different from one with Domain defined.
However, when I ran experiments on chrome and firefox, I found out that this was not the case. Browsers only seem to recognize cookies as different when Path attribute is non blank and not /
Here is the code that I used for the experiment. I used express but I am directly setting the set-cookie header, so there should be no library-specific behavior.
index.mjs
import express from "express";
const app = express()
app.get("/",(req,res)=>{
res.send("front page");
});
const inspect = function(req,res){
res.send(req.headers.cookie);
};
app.get("/inspect",inspect);
app.get("/subdir/inspect",inspect);
app.get("/bar1",(req,res)=>{
res.append("Set-Cookie", "foo=bar1;")
res.send("set foo to bar1");
});
app.get("/bar2",(req,res)=>{
res.append("Set-Cookie", "foo=bar2;")
res.send("set foo to bar2");
});
app.get("/bar3",(req,res)=>{
res.append("Set-Cookie", "foo=bar3; Domain=localhost; Path=/;");
res.send("set foo to bar3 with attrs");
});
//bar1, bar2, and bar3 gets treated the same
app.get("/bar4",(req,res)=>{
res.append("Set-Cookie", "foo=bar4; Domain=localhost; Path=/subdir;");
res.send("set foo to bar4 with path /subdir");
});
//bar4 gets treated differently as expected
app.get("/clear",(req,res)=>{
res.append("Set-Cookie", "foo=bar1; expires=Thu, Jan 01 1970 00:00:00 UTC;");
res.append("Set-Cookie", "foo=bar2; expires=Thu, Jan 01 1970 00:00:00 UTC;");
res.append("Set-Cookie", "foo=bar3; Domain=localhost; Path=/; expires=Thu, Jan 01 1970 00:00:00 UTC;");
res.append("Set-Cookie", "foo=bar4; Domain=localhost; Path=/subdir; expires=Thu, Jan 01 1970 00:00:00 UTC;");
res.send("cleared all cookies");
});
app.listen(3020);
on console at localhost:3020/
console.log(await (await fetch("/clear")).text());
console.log(await (await fetch("/bar1")).text());
console.log(await (await fetch("/subdir/inspect")).text());
console.log(await (await fetch("/bar2")).text());
console.log(await (await fetch("/subdir/inspect")).text());
console.log(await (await fetch("/bar3")).text());
console.log(await (await fetch("/subdir/inspect")).text());
console.log(await (await fetch("/bar4")).text());
console.log(await (await fetch("/subdir/inspect")).text());
console output
cleared all cookies
set foo to bar1
foo=bar1
set foo to bar2
foo=bar2
set foo to bar3 with attrs
foo=bar3
set foo to bar4 with path /subdir
foo=bar4; foo=bar3
Why does this happen? Is this specific to localhost (but in that case, what about blank vs / Path)? Also how reliable is this behavior?
Edit:
I found out that empty or invalid Path field gets set to "/". That answers the path part of this question
The exact algorithm is written under 5.1.4. Paths and Path-Match on the previously mentioned RFC document