The correct place for only, as for other adverbs, is next to (preferably immediately before) the word it qualifies. But only is a wayward word. It is much given to deserting its post and taking its place next the verb, regardless of what it qualifies. It is more natural to say "he only spoke for ten minutes" than "he spoke for only ten minutes". The sport of pillorying misplaced onlys has a great fascination for some people, and opportunity for indulging in it is never far away. A recent book, devoted to the exposing of errors of diction in contemporary writers, contained several examples such as:
He had only been in England for six weeks since the beginning of the war.
This only makes a war lawful: that it is a struggle for Law against Force.
We can only analyse the facts we all have before us.
These incur the author's censure. By the same reasoning he would condemn Mr. Churchill for writing in The Gathering Storm:
Statesmen are not called upon only to settle easy questions.
Fowler took a different view. Of a critic who protested against "he only died a week ago" instead of "he died only a week ago" Fowler wrote:
There speaks one of those friends from whom the English language may well pray to be saved, one of the modern precisians who have more zeal than discretion . . .
So do not take too seriously those I have elsewhere called "the only-snoopers". But be on the alert. It will generally be safe to put only in what the plain man feels to be its natural place. Sometimes that will be its logical position, sometimes not. Sometimes a natural but ungrammatical position is a positive aid to being understood; it prevents the reader from being put on a wrong scent. In the sentence "The temperature will rise above 35 degrees only in the south-west of England", only is carefully put in its right logical place. But the listener would have grasped more quickly the picture of an almost universally cold England if the announcer had said "the temperature will only rise above 35 degrees in the south-west of England".
A purist might condemn:
I am to express regret that it has only been possible to issue a licence for part of the quantity for which application was made.
but the ordinary reader will think that this conveys the writer's meaning more readily and naturally than:
I am to express regret that it has been possible to issue a licence for only part of the quantity for which application was made.
But it cannot be denied that the irresponsible behaviour of only does sometimes create real ambiguity. Take such a sentence as:
His disease can only be alleviated by a surgical operation.
We cannot tell what this means, and must rewrite it either:
Only a surgical operation can alleviate his disease (it cannot be alleviated in any other way),
or:
A surgical operation can only alleviate his disease (it cannot cure it) .
Again:
In your second paragraph you point out that carpet-yarn only can be obtained from India, and this is quite correct.
The writer must have meant "can be obtained only from India", and ought to have so written, or, at the least, "can only be obtained from India". What he did write, if not actually ambiguous (for it can hardly be supposed that carpet-yarn is India's only product), is unnatural, and sets the reader puzzling for a moment.