What do 即 (jí) and 已 (yǐ) do in the sentence 病征在成年早期即已显露 ("symptoms become visible at early adulthood")?

Question

In a document about 边缘性人格障碍 (biānyuán xìng réngé zhàng'ài) = "Borderline Personality Disorder", we have the following sentence:

病征在成年早期即已显露，但随年龄增长趋于缓和或稳定。
_{Bìngzhēng zài chéngnián zǎoqí jí yǐ xiǎnlù, dàn suí niánlíng zēngzhǎng qū yú huǎnhé huò wěndìng.}

I translate this to:

Symptoms become visible at early adulthood, but with age they have an increasing tendency to alleviate or stabilize.

I think it's a reasonably accurate translation. (Google Translate gives a translation that's much the same: "Symptoms are revealed early in adulthood, but tend to ease or stabilize with age.")

What I'm confused about is the use of

• 即 (jí), which means something like "namely" (also mentioned in What does 即 mean in this sentence?), but I don't think that makes sense here, and
• 已 (yǐ), which means something like "already".

Neither of these makes sense to me in this context.

Question: What do 即 and 已 do in the sentence 病征在成年早期即已显露?

There's a few examples of 即已 used together on YouDao, but I don't see how they help.

Answer 1

即 in this context means 即刻: "immediately; at once; instantly"

已 = already; had

即已 = had immediately

即已显露= had immediately shown

Edit:

就 can also means "immediately"

• 黎明[即]起 = Wake up [as soon as] dawn arrives

• 黎明[就]起床 = wake up [as soon as] dawn arrives

Answer 2

病征在成年早期即已显露

即 here means 就. It means this sense:

So, 病征在成年早期即已显露 is equal to say 病征在成年早期就已显露.

Answer 3

即已 = 就已经

病征在成年早期即已（就已经）显露，
Symptoms are already apparent in early adulthood
但随年龄增长趋于缓和或稳定。
but with age tend to moderate or stabilize.