One more inconclusive evidence for my theory.

[Optimism is my Phil-osophy]

In Lemony's secret letter to his "sister" in TSS chapter 5, Lemony wrote:
"Try to get us a room without ugly curtains."

However, at the time of the main events narrated by Lemony, Hotel D had no curtains.
Hotel D had shutters.

Chapter 2 of TPP states:
"Below the sign, farther from the orphans, was a row of windows with the number 9 emblazoned on each of their shutters"
...
Below this row of windows was another with the number 8 emblazoned on the shutters.

Chapter 10:
"The Baudelaire orphans gazed at the settling surface of the pond and saw the reflections of shutters and windows opening on every story of the Denouement Hotel."

This is further evidence that Hotel D was different at the time Lemony wrote the letter. This collaborates with my theory that the TSS secret letter was written many years after the events described in TSS. During these years the hotel was rebuilt and they placed courtains on the windows. Of course, this will not convince some people, who will evidently be upset to have to try to convince me that Daniel Handler has made chronological mistakes ... While I will continue in my lonely struggle to show that people who use the artifice to blame mistakes Handler's chronological notes to justify any apparent contradiction are missing an exciting and chronologically separated parallel story for many years from the main events narrated in ASOUE. A good story that I believe was designed by Daniel Handler ... I just can't prove it, which is a pity.

[Dante]

Setting aside the obvious fact that Handler hadn't decided on the exact appearance of the Hotel Denouement rooms at the time of writing - indeed, consider also the possibility that Lemony has never been to the Hotel Denouement and only assumes that they use curtains - it's also not impossible for a window to use both curtains and shutters at once.

[Optimism is my Phil-osophy]

Nov 9, 2019 12:17:53 GMT -5 Dante said:

it's also not impossible for a window to use both curtains and shutters at once.

You are the second person who tells me that today, Dante

Because of this I went to get the scene where Klaus laid the birdpaper in the sauna window. Note the scene description:
TPP chapter 5:

"Without another word, the manager left, and Klaus was alone in the sauna. Carefully, he walked through the steam and felt his way to the window, which he managed to unlatch and open, swinging a shutter marked out over the pond. Aswill happen when a very hot room is exposed to cold air, the steam raced through the window and evaporated. "

Courtains are not mentioned. Just shutters are mentioned.

[Dante]

Absence of evidence is not evidence of absence - though as I'm sure you understand, I don't believe that there were curtains there, either. I merely think the author's mental image underwent refurbishment. But perhaps some floors do use curtains instead of shutters; who knows?

[Optimism is my Phil-osophy]

That's true ... after all Courtains in saunas would get wet. The "inclusive" part involves these aspects. But I will include this text in the "auxiliary evidence" section in my commonplace book.